In the literature there appears to be variability in reported levels of certain hormones during haemorrhage, specifically adrenocorticotrophic hormone (ACTH) and beta-endorphin. It is possible that this variability may be due to the choice of anaesthetic. Therefore, the effect of 3 common research-only anaesthetic agents (alphaxalone alphadolone, propofol, and pentobarbitone) on ACTH and beta-endorphin levels during haemorrhage was assessed in pigs. Animals were divided into 3 groups: group I received alphaxalone alphadolone (n = 5), group H received propofol (n = 6), and group III received pentobarbitone (n = 6). Pigs were subjected to a continuous fixed-volume haemorrhage under one of the above anaesthetics while being mechanically ventilated. ACTH and beta-endorphin levels increased significantly during haemorrhage under propofol and pentobarbitone anaesthesia but not with alphaxalone alphadolone. For ACTH there was no significant difference between the groups, whereas for beta-endorphin there was a significant difference between the propofol- and pentobarbitone-anaesthetized pigs. The increase in heart rate during haemorrhage was significantly different between the alphaxalone-alphadolone and propofol as well as between the propofol and pentobarbitone groups. The drop in blood pressure was only significantly different between the alphaxalone-alphadolone- and propofol-anaesthetized pigs. These results indicate that the choice of anaesthetic agent can affect the hormone response to haemorrhage and may account for the variable hormone levels reported in the published literature to date.